Leakage tests are used to test integrated circuits after they have been fabricated to find defects and to improve manufacturing processes, handling processes and packaging processes. Such integrated circuits are formed on a die and typically installed into a package. The die may be tested before or after it is installed into a package. The package typically has pins or bumps to connect to a circuit board or a socket and so the die may be tested directly inside the package or after being placed onto a circuit board or into a socket. DC (Direct Current) tests for I/O (Input Output) pins include leakage tests, Vix/Vox tests and Opens/Shorts test. Vix/Vox is used to characterize the DC behavior of the transmitter and receiver interfaces. Vix refers to the upper and lower voltage limits of an input and Vox refers to the upper and lower limits of an output. Opens/shorts testing tests for the presence of open circuits and short circuits. This testing can be used to ensure the reliability of the package assembly process and the connectivity of bumps to mapped pins. Bumps on the inside of a package connect to pins on an integrated circuit.
No Touch Leakage (NTL) tests have been used to save on tooling costs when the number of pins to be tested on an integrated circuit package is more than is available on commonly available test modules. One NTL test looks at RC (Resistance-Capacitance) decay and another looks at DC bias, however, both tests suffer from process variability, have difficulty in achieving high accuracy without significant effort and have very long test times, approaching several milliseconds.
ICDCT is a Reduced Pin Count Test (RPCT) as it connects to tens to hundreds of Pin Under Test via couple of pins. There are several sources of error in applying analog bus tests to DC testing. The sources of error include the IR (Voltage=Current*Resistance product) drop that occurs based on the pin location on the bus that is being tested, the leakage of the pins used to make contact to conduct the tests and the leakage of multiplexers that receive the test signal. The IR drop can easily reach 100 mv or higher making it challenging to reliably determine upper and lower functioning limits across all of the I/O (Input/Output) pins of a multiple pin interface. The multiplexer leakage and pin leakage can reach 100's of micro amps. This can be as large as the pin leakage that is to be measured, obscuring the test results.
The limitations of NTL and RPCT methods have reduced their use. As a result, testers with PMU (Parametric Measurement Unit) are often used for leakage tests. However, PMU testers must be independently connected to each pin that is to be tested, increasing the cost. The analog measurement increases the time required for the tests.